The invention relates to a web guiding structure in a drying section, downstream from a coating device and having suspension and infrared dryers. Such a device is described in the German patent publication 3,910,898 A, so that the combination of infrared and suspension dryers is known.
One object of the invention is connected with the problem of so guiding the web of paper or board after coating thereof, while it still has a moisture content of approximately 30%, that the web is dried and the web is subjected to minimum stresses and only has a minimum tendency to form folds, more particularly in the longitudinal direction. There has been a proposal in the European patent 236,819 to bend a web relatively sharply along an arc in a contact-free manner by a rigid, beam-like air chest with air blowing elements in order to prevent the wet material of the coating composition sticking to a roll as is otherwise utilized for bending and guiding the web.
The object of substantially reducing web corrugations in the transverse direction and of preventing the development of folds is to be attained using the features of the present invention. Web corrugation in the transverse direction means that the corrugations (crests and troughs) follow each other in the transverse direction of the web.
In order to better stabilize the course of the web it is possible to provide a beam-like air plenum or chest with jets upstream from the deflecting device, and directed against the outer side of the web arc.
Preferably this beam-like device is curved, there then additionally being a more powerful blowing action at the center of the web than at its edges so that there is a more pronounced curvature or bending in the center than at the edges and therefore a tendency to stretch it in the breadth direction.
Furthermore, it is appropriate as well if the drying is substantially performed to completion, there being an alternating succession of infrared and suspension dryers, an optimum maximum drying being achieved in the shortest possible distance.
Although there has been a proposal in the European patent publication 0 291 832 to have an alternating succession of infrared and suspension dryers, this was not for the same purpose as in the present invention, that is to say smoothing the web by guiding at along an undulating path. Accordingly, the suspension dryers in this case have such a design that the web is not caused to undulate but is rather more guided along a straight path at a very regular distance from the infrared dryers in order to make best use of their heating effect. After each infrared dryer a suspension dryer is arranged for the removal of the water vapor, which is formed under each infrared dryer. The dryers are arranged on only one side of the web.